Photovoltaic (PV) cells provide a renewable source of electrical energy. When PV cells are combined in an array such as in a PV module, the electrical energy collected from all of the PV cells can be combined in series and parallel arrangements to provide power with a certain voltage and current. Many recent design and engineering advances have increased the efficiency and functionality of PV modules.
One area of development focuses on collecting the electrical energy from all of the PV cells in a PV module so that the collected electrical energy can be efficiently transferred to an electrical load connected to the PV system. For example, SunPower Corporation of San Jose, Calif., offers a highly efficient solar cell design which locates the metal contacts needed to collect and conduct electricity on the back surface of the PV cells so that cell interconnections do not block incident sunlight.
Another area of development relates to wiring techniques which might lower the manufacturing cost of PV module components and facilitate a better design layout of such components on the PV module. FIG. 1 illustrates a conventional busbar 10 for a PV module. The illustrated conventional busbar 10 includes an interconnect bus 12, a plurality of individual bus tabs 14, and a linear terminal bus 16. Different busbar designs may implement fewer or more bus tabs 14 than shown. The individual bus tabs 14 are typically soldered or welded to the interconnect bus 12 at corresponding solder or welding joints 18. The linear terminal bus 16 is soldered to the interconnect bus 12 at a similar solder or welding joint 18. The bus tabs 14 connects to electrical contacts or ribbons for each row of PV cells, and the terminal bus 16 connects the interconnect bus 12 to a junction box on the PV module.
FIG. 2 illustrates another conventional busbar 30 for a PV module having back contact cells. The conventional busbar 30 of FIG. 2 is similar to the conventional busbar 10 of FIG. 1, except that the conventional busbar 30 does not have a terminal bus 16. These types of conventional busbars 30 are typically used to connect adjacent rows of PV cells to one another. Other types of cell interconnects are used to connect individual PV cells to one another within the rows of PV cells.
Wire flattening is another conventional technology to form busbars. Wire flattening employs a bending machine to bend wire into a specified shape and then a flattening machine to flatten the shaped wire into a flattened sheet having a shape corresponding to the shaped wire.
Some conventional busbars suffer from several disadvantages. For example, the use of linear components in conventional busbars results in relatively long electrical path lengths and, hence, increased voltage drop between the rows of PV cells and the junction box.
Also, the design and layout of conventional busbars is typically limited by the availability of conductive ribbons. If multiple ribbon sizes are used, then the inventory costs of purchasing, storing, and handling the various ribbon sizes are increased. On the other hand, if only one ribbon size is used, the design and layout of the conductive paths is limited by the physical characteristics (e.g., width, thickness, etc.) of the available ribbon.
Conventional busbars also implement several solder or welding joints for each busbar (e.g., seven joints for the conventional busbar 30 of FIG. 1). These joints are sources of potential physical failure of the busbar. The thickness of these joints also creates stress on the corresponding PV cells, which can break and become useless. For example, the joints can add extra stress on the PV cells during module manufacturing, and the PV cells can crack, which degrades cell performance. Such breakage is frequently at the edges of PV cells because the linear configuration of conventional busbars results in a portion of the conventional busbar extending beyond the edge of the typically cropped corners of the PV cells. Additionally, the cost of assembly of conventional busbars is relatively high because the fabrication process implements multiple solder or welding joints for each conventional busbar.